324 NATURE-STUDY REVIEW [10:3— Nov., 1914 



species of hydra regenerate when cut as above described, but if 

 you cut a green hydra in half and a brown hydra in half, then pin 

 the upper half of, say, a green hydra to the lower half of a brown 

 hydra, using a bit of bristle as a pin, the cut surfaces will grow 

 together and you will have a hydra half green and half brown. 

 Many of these experiments in regeneration are described in these 

 old books on hydra. 



You will be quite sure to find some of the hydra in your jars 

 that are growing their young by a process called budding. A little 

 bulge appears on one side of an adult hydra. This grows larger 

 and larger, the body cavity of the parent extends up into this 

 extension that is to be the young animal. Bye and bye tentacles 

 appear, a mouth breaks through at the upper end of the biilge and 

 it is evident that a little hydra is growing on the side of the parent. 

 Sometimes this young one will grow to maturity and produce young 

 on itself before it detaches from the old hydra. 



You will surely find a good many other interesting animals as 

 you are looking for hydra and studying it. If you can have a 

 little pocket lens to help you you will, in the course of a few weeks 

 work with this tumbler aquarium, be able to draw and make record 

 of an exceedingly interesting lot of animals. These animals, too, 

 are of large economic importance for it is these tiny forms, espec- 

 ially the crustaceans, little relatives of the common crayfish and 

 lobster, that form the bulk of the food of the smaller fishes. 



Editorial 



Need of Purposeful Observation in Nature-Study 



One of the great needs in teaching nature-study is some definite 

 aim to guide children in their observation of materials. The 

 teacher should always have in mind the general aims of education 

 and the special function of nature-study, but it is equally impor- 

 tant that the child should have in mind some definite purpose for 

 each lesson. Too much observation is carried on without any 

 specific purpose, other than the meaningless one of observing 

 everything that can be seen about the material in hand. When 

 educators held the disciplinary aim of education, in accordance 

 with which the chief aim of nature-study was to develop the power 

 of observation, there seemed some justification for this aimless 



